1. Field of the Invention
The present invention relates to a structure of infrared (IR) detector and a fabrication method thereof, and in particular to the two-color(dual band) IR detector.
2. Description of the Backgound Art
One of the most interesting and challenges in the field IR detectors is the realization of single chip multi-spectral detectors for many applications. This is because improved IR system flexibility and capability can be realized through the use of multi-spectral sensor and imaging arrays. Simultaneously and independently operable single chip multi-color sensor and imaging arrays are required for small size and compact applications for tracking rapidly moving objects.
The evolution of epi-layer growth technology yields multi-layer IR sensitive materials on the proper substrate. Owing to the advent of the multi-layer HgCdTe wafer, single chip HgCdTe infrared focal plane array (FPA) concepts for dual band detection (two color detection) have been developed. Two configurations which can be realized using multi-layer HgCdTe have been attractive. The first one is bias selectable two color HgCdTe IR detectors (we called BSTCD) which was disclosed in Journal of Vacuum Science & Technology B 10, (1992) 1626-1632. The second is independently accessible two color IR detectors (also called IATCD) disclosed in Journal of Electronic Materials 24, (1995) 669-679. These two concepts are based on the multi-layer heterostructure utilizing HgCdTe of desired spectral bands.
The structure of BSTCD and is N-P.sup.+ -n, is operated by biasing between the two terminals. One bias polarity results in LWIR (long wavelength IR, 8-14 .mu.m) detector response, while the opposite polarity results in MWIR (middle wavelength IR, 3-5 .mu.m) detector response. This device was realized with three layer Hg.sub.(1-x) Cd.sub.(x) Te grown by molecular beam epitaxy.
Even though the bias selectable dual-band HgCdTe IR detector affords perfect spatial collocation of the two detectors, it has the inherent drawback of not allowing temporal simultaneity of detection. Either one or the other photodiode is functioning, depending on the bias polarity applied across the back-to-back pair. Other problems also arise from the fact that it does not allow independent selection of the optimum bias for each photodiode, and that there can be substantial MW crosstalk in the LW detector due to injection from the floating forward-biased MW photodiode into the LW photodiode.
Recently, a true independently accessible two-color IR detector (IATCD) was successfully demonstrated. The IATCD provides independent electrical access to each of two spatially collocated back-to-back photodiodes so that true simultaneous and independent detection and integration of MW and LW photocurrents are also accomplished.
However, the above described IATCD is a p-n-N-P structure formed by four Hg.sub.(1-x) C.sub.(x) Te layers grown sequentially onto a CdZnTe substrate. The sequential growth of four HgCdTe layers is very hard to implement with current HgCdTe growth techniques. Thus, low yield and high cost concerns are critical drawbacks of this manufacturing procedure.
Therefore, in the present invention, the new structure of two-color IR detector and its fabrication method to overcome the aforementioned problems are provided.